Dyer Lee A, Letourneau Deborah K
Western Colorado Center for Tropical Research, Mesa State College, Grand Junction, CO 81502, USA e-mail:
Oecologia. 1999 May;119(2):265-274. doi: 10.1007/s004420050785.
We tested integrative bottom-up and top-down trophic cascade hypotheses with manipulative experiments in a tropical wet forest, using the ant-plant Piper cenocladum and its associated arthropod community. We examined enhanced nutrients and light along with predator and herbivore exclusions as sources of variation in the relative biomass of plants, their herbivores (via rates of herbivory), and resident predaceous ants. The combined manipulations of secondary consumers, primary consumers, and plant resources allowed us to examine some of the direct and indirect effects on each trophic level and to determine the relative contributions of bottom-up and top-down cascades to the structure of the community. We found that enhanced plant resources (nutrients and light) had direct positive effects on plant biomass. However, we found no evidence of indirect (cascading through the herbivores) effects of plant biomass on predators or top predators. In contrast, ants had indirect effects on plant biomass by decreasing herbivory on the plants. This top-down cascade occurred whether or not plant resources were enriched, conditions which are expected to modify top-down forces.
我们在一片热带湿润森林中，利用蚁栖植物钟叶胡椒及其相关节肢动物群落，通过操纵实验来检验自下而上和自上而下的综合营养级联假说。我们研究了养分和光照增强以及捕食者和食草动物排除等因素，将其作为植物、食草动物（通过食草率）和常驻捕食性蚂蚁相对生物量变化的来源。对二级消费者、一级消费者和植物资源的联合操纵，使我们能够研究对每个营养级的一些直接和间接影响，并确定自下而上和自上而下的级联对群落结构的相对贡献。我们发现，增强的植物资源（养分和光照）对植物生物量有直接的正向影响。然而，我们没有发现植物生物量对捕食者或顶级捕食者有间接（通过食草动物级联）影响的证据。相比之下，蚂蚁通过减少对植物的食草作用，对植物生物量产生了间接影响。无论植物资源是否丰富，这种自上而下的级联都会发生，而植物资源丰富的条件预计会改变自上而下的作用力。
